Re: [PATCH v1 1/8] docs: documentation and schema for the new TPM Proxy device

On 5/8/20 8:06 AM, Daniel Henrique Barboza wrote: > QEMU 4.1.0 introduced a new device type called TPM Proxy, currently > implemented by PPC64 guests via a new virtual device called > 'spapr-tpm-proxy' (see QEMU 0fb6bd073230 for more info). > > The TPM Proxy device interacts with a TPM Resource Manager, a host > device capable of multiplexing the host TPM with multiple processes. > This allows multiple guests to access some TPM features at the > same time. Note that this mode of operation does not provide > full TPM features to be available for the guest - for that case > the guest still needs to assign a vTPM device (tpm-spapr for > PPC64 guests). Although redundant, there is currently no technical > limitation for a guest to assign both a vTPM and a TPM Proxy at the > same time. > > This patch adds documentation and schema for the new TPM Proxy device. > An example of a TPM Proxy device connected to a TPM Resource Manager > '/dev/tpmrm0' will look like this: > > <tpmproxy model='spapr-tpm-proxy'> > <device path='/dev/tpmrm0'/> > </tpmproxy> We already have:     <backend type='passthrough'>       <device path='/dev/tpm0'/>     </backend> Now what is the difference between this tpm-proxy device using /dev/tpmrm0 and having the existing passthrough device use /dev/tpmrm0?  Is there any useful filtering going on by the tpm-proxy device? If not, why not use passthrough with /dev/tpmrm0?